1. Field of the Invention
The present invention is directed to improved flexible vacuum bellows or expansion joints for interconnecting flanged pipe sections. More particularly, this invention relates to an improved flexible expansion joint designed to operate under high vacuum and at relatively high temperatures and to function in acid or other highly corrosive fluid service.
2. Description of Prior Art
Materials that have been employed as flexible membranes in expansion joints in acid service include trifluoroethylene sold under the KEL-F trademark and polytetrafluoroethylene (TFE) which is sold under a variety of trademarks such as "TEFLON", "HALON", "FLUON", and others. For prior art expansion joints suitable for such service, see Lewis, U.S. Pat. No. 3,527,481 and Press et al, U.S. Pat. No. 3,633,945. The chief disadvantage of the flexible membranes employed in the prior art expansion joints is that they are all under compression, i.e., the membrane comprises one or more U-shaped convolutions which extend radially outward from the joint which would cause the membrane to collapse if employed in vacuum service.
In each of the prior art expansion joints for high pressure service, metallic expansion limiting rings are provided to prevent radial expansion of the flexible membrane. Internal metallic rings are also provided to prevent collapse in similar types of expansion joints comprising TFE materials for vacuum service. Bawcom et al, U.S. Pat. No. 3,139,115 is representative of the prior art for such vacuum bellows.
In one design of an expansion joint, flexible membranes having inwardly extending U-shaped convolutions are employed in an entirely different manner and for an entirely different purpose than that employed in the present invention; see Hall, U.S. Pat. No. 1,992,612. In the prior art expansion joint, a tubular membrane of a ductile metal possessing a high elasticity and durability is secured between a wall of an inner cylindrical joint member and an end ring of an outer cylindrical joint member. When the expansion joint is under conditions of expansion, the high pressure within the pipe sections is transmitted from the joint to the portion of an annular chamber between the inner wall of the outer expansion member and the inwardly extending convolution of the flexible member. Such an expansion joint is inapplicable to operation under vacuum since the convolutions would collapse to the inner wall of the outer flexible membrane.